Definition
An engine malfunction in which the engine accelerates uncontrollably beyond its normal operating range, with the pilot unable to reduce power through normal throttle inputs. In piston engines this is typically caused by a failed governor or propeller pitch control allowing RPM to rise without limit; in turbine engines it usually involves a failure in the fuel control unit that allows excess fuel flow.
Plain English
The engine speeds up on its own and the pilot can't slow it down with the throttle. It keeps revving higher and won't respond to normal controls.
Context Anchor
Seen in accident, emergency, and instructional discussions about engine control problems, especially during engine start, taxi, or high-power operation.
Derivation
From 'run away,' meaning to escape control. The engine has effectively escaped the pilot's ability to control it — it is running on its own, beyond commanded power.
Why Pilots Care
A runaway engine can quickly exceed safe operating limits, risking engine or propeller damage and requiring immediate corrective action such as throttle reduction or feathering.
Grounding Statement
A runaway engine is an engine that is no longer responding normally when the pilot tries to reduce its speed or power.
Intuition Check
Runaway does not mean the engine separates from the airplane. It means the engine’s speed or power has run away from normal control.
Example Sentence 1
During cruise the propeller RPM climbed past redline and the throttle had no effect, so the pilot ran the runaway engine checklist and shut it down.
Example Sentence 2
During the preflight briefing the instructor explained how to recognize and respond to a runaway engine in flight.